1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a back light assembly for a liquid crystal display device.
2. Discussion of the Related Art
Generally, a cathode ray tube (CRT) is mainly used in monitors for information terminals and measuring instruments as well as a television. It has been difficult to miniaturize and reduce the weight of the CRT. Thus, a liquid crystal display device has been actively developed that is small in size and light weight and with low power consumption. Recently, the liquid crystal display device, which is a flat panel display device, has been used as a display for a laptop computer, a monitor for desktop computer, a large monitor of 30 inches or greater, and a wall-mount TV. The demand for the liquid crystal display device is increasing.
Such a liquid crystal display device is a light-receiving device which displays an image by controlling the quantity of external light. Accordingly, a separate light source, i.e., a back light assembly for irradiating light to a liquid crystal display panel, is required.
The back light assembly is classified into an edge type and a direct type depending on the position of the light source against a display area. The direct type back light assembly is widely used in a large sized liquid crystal display device of 30 inches or greater because it has high light transmittivity, it is easy to handle and it does not have a limitation in the size of the display area.
The direct type back light assembly does not require a light guide plate, which directs linear light from a light source (lamp) to the display surface. The direct type back light assembly includes a plurality of lamps, a reflection sheet and a diffusion plate. The lamps are provided at a lower portion of the display area. The reflection sheet reflects light irradiated from the lamps in the display area so as to avoid loss of light. The diffusion plate diffuses light in an upper portion of the lamps to emit uniform light.
Here, because a considerable amount of space exists between the lamp and the diffusion plate, the diffusion plate drops down due to its own weight and/or high temperature. To prevent the diffusion plate from dropping down, a plurality of supports are provided between the diffusion plate and the reflection sheet.
A support structure of the diffusion plate of a direct type back light assembly in the related art will be described with reference to the accompanying drawings.
FIG. 1 is a partial sectional view showing a support structure of a diffusion plate of a direct type back light assembly in the related art.
As shown in FIG. 1, a support 6 is provided between a reflection sheet 4 and a diffusion plate 5. A prism sheet 8 is provided on an upper surface of the diffusion plate 5 to improve the luminance of a liquid crystal display panel 9 by converging light diffused through the diffusion plate 5. The liquid crystal display panel 9 is provided on an upper portion of the prism sheet 8 to display data. A plurality of lamps (not shown) are provided in a space between the reflection sheet 4 and the diffusion plate 5.
The support 6 is made of a rigid material such as poly-carbonate to sufficiently prevent the diffusion plate 5 from dropping down. Also, the support 6 has a pointed shape at one end to minimize the amount of area covering the display area.
However, the aforementioned support structure of the diffusion plate has several problems. If an external impact or oscillation is applied to the liquid crystal display device, foreign materials or scratches occur on a contact area between the diffusion plate and the support due to friction between them. The foreign materials or scratches act on the display area leading to poor image quality.
In addition, since the support has a pointed end portion, the end portion may be broken or deformed due to such external impact. In this case, the support cannot prevent the diffusion plate from dropping down. To solve such a problem, the support may be of a soft material such as a rubber. In this case, however, the support cannot sufficiently support the diffusion plate due to reduced rigidity.